Identical Twins Prioritize Their Co-Twins

A 2015 peer-reviewed psychology study asked 515 adults to compare their attachment to a sibling with their attachment to a romantic partner. Identical twins ranked their co-twin significantly above their partner, with average hierarchy positions of 1.42 and 2.10, respectively. Fraternal twins ranked their co-twin and partner about equally, while non-twin siblings clearly placed their romantic partner first.

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